Heretofore, a heat insulating member 3 (FIG. 2) formed by laminating alumina-silica ceramic fiber sheets each having a composition ratio of alumina (Al2O3) to silica (SiO2) of 50:50 has been used as a heat insulating member for a portion of an end cone e (FIG. 1) consisting of an outer cone 1 and an inner cone 2. There are heat insulating members as disclosed, for example, in JP-A-11-117731, U.S. Pat. No. 5,250,269 and the like.
Recently, the revolution number of the engine tends to increase with the high output of the engine, and also the displacement of the engine is made small accompanied with the fuel saving of the engine and hence it tends to raise the output by increasing the revolution number. Under such situations, the temperature of the exhaust gas rises in the driving of the engine, and as a result, the temperature of the exhaust gas becomes recently 900-1000° C. as compared with the conventional temperature of about 700-900° C. The contents of JP-A-11-117731, U.S. Pat. No. 5,250,269 are incorporated here in by reference in their entirety.